This invention relates to a disk gripper and, more particularly, to a device for gripping a disk such as a magnetic disk memory or a substrate of a semiconductor device lying on a horizontally disposed polishing sheet of a disk polisher.
Disks which are used as magnetic memory devices are generally circular with a circular center hole and of a uniform thickness except along their outer and inner edges. During their production process, they are usually transported from one work station to another in a cage-like cassette, standing up vertically therein and being kept parallel to and separated from one another. The device for polishing the surfaces of these disks may be referred to as a disk polisher and FIG. 1 shows an example of such a device characterized as having a polishing sheet 11 over a horizontal plate and a plurality (five according to the illustrated example) of circular carriers 12 placed on this polishing sheet 11. Each carrier 12 is formed as a gear wheel and has several (eight according to this example) circular holes 13 formed therethrough such that disks to be polished can be individually accommodated in these holes 13. These carriers 12 are enclosed inside a geared circular inner wall 14, individually engaging therewith, and there is a sun gear 15 at the center of this circular wall 14. The sun gear 15 is connected with a rotary power source such as a motor (not shown) and engages with each of the carriers 12 such that, as the sun gear 15 is rotated with the wall 14 fixed, the carriers 12 rotate around the sun gear 15 while rotating around their own central axes. If the holes 13 of the carriers 12 are filled with disks to be processed, these disks are pushed by the inner walls of the holes 13, sliding over the polishing sheet 11, as the carriers 12 undergo their rotary motions. The top surface of the polishing sheet 11 is preliminarily covered with a polishing agent containing water and the disks are thus polished as they slide over this surface. After one side of each disk is thus polished, the disks are picked up and turned over to have the other sides similarly polished.
After the disks are polished by means of a polisher of the type described above, the disks tend to get stuck with the top surface of the polishing sheet 11 and it is therefore not always easy to lift up the disks, for example, to collect them into a cassette to be transported to another work station. Since the disks used as substrates of semiconductor devices are fragile and easily contaminated, a robotically operated device capable of gripping and removing a disk is generally desirable but the polishing sheet 11 does not remain perfectly flat after a repeated use and the carriers do not always move in a perfectly horizontal plane. As a result, the individual disks to be removed from the disk polisher are not necessarily at the same height. This makes the operation very difficult for a conventional automated disk-handling device.